-

ARIZONA W ATE R COMMISSION

BULLETIN 3

HYDROLOGIC REGIMEN OF

LOWER TONTO CREEK BASIN GILA COUNTY, ARIZONA A RECONNAISSANCE STUDY

BY H.H. SCHUMANN AND B. W. THOMSEN

PREPARED BY THE GEOLOGICAL SURVEY UNITED STATES DEPARTMENT OF THE INTERIOR

'Waler Rights Adjudication ream eMl Division

PHOENIX, ARIZONA NOVEMBE R 1972

This report has been designated as an Arizona Water Commission bulletin by permission of Wesley E, Steiner, Executive Director of the Arizona Water Commission, The Water Commission has approved the addition of this report to the bulletin series to promote widespread avail­ability of the d a t a necessary to sound management and optimum utilization of Arizona's water resources, The Commission has not participated in either the collection and compilation of the data or in the preparation and du­plicating of the report,

Abstract .•• Introduction

CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose of the investigation. Methods of the investigation. Location, topography, and drainage Climate .................. .

Rock units and their water- bearing properties Igneous and metamorphic rocks Sedimentary rocks

Basin fill Alluvium

Hydrology •••••• • Streamflow .•

Low flows. • Tributary flows Infiltration of streamflow Flow to Roosevelt Lake .••

Ground water . . . . . . . . . . . Occurrence and movement. Recharge ........... .

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•

Infiltration of streamflow •

•

• •

•

•

• •

Infiltration of precipitation and irrigation water Discharge .............. .

Water losses by evapotranspiration. Potential evapotranspiration Evapotranspiration losses

Chemical quality of water Summary and conclusions •• References cited ••••••

• • •

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• •

ILLUSTRATIONS

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• • •

• • • • • •

• • • • • •

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• •

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• • • •

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Figure 1. Map showing area of rep 0 r t and Arizona I s water provinces .' .........................•

2. Sketch showing well-numbering system in Arizona.

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Page

1 2 2 2 5 5 6 8 8

11 12 13 15 15 20 20 20 21 21 21 23 23 26 27 28 31 32 34 38

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IV CONTENTS

Page

Figure 3. Graph showing average m 0 nth 1 y precipitation, pan evaporation, and potential evapotranspiration in and near the lower Tonto Creek basin .•..•..•••• 7

4. Generalized geologic map of the lower Tonto Creek basin .. "" .. <> ................................ " " " .......... ..

9

5. Diagrammatic sketch of the hydrologic system in the lower Tonto Creek basin •. . • • • • • • . • . . • • • • 14

6-9. Graphs showing:

.6. Annual flow of Tonto Creek above Gun Creek, near Roo s eve It, Ariz., 1942 - 70 water year s .. .. .. .. .. .. .. .. .. .. .. .. .. " " .. .. .. .. .. .. .. .. .. .. 16

7. Average monthly flow of Tonto Creek above Gun Creek, near Roosevelt, Ariz., 1942-70 water years .. .................... " .... " .. " " " " .. 17

10.

8. Flow-duration curve for Tonto Creek above

9.

Gun Creek, near Roosevelt, Ariz., 1942-70 water years ...... " ..........

Low-flow frequency curves for Tonto Creek above Gun Creek, near Roosevelt, Ariz. ..

Diagrammatic sections s how i n g gaining and losing reaches of lower Tonto Creek •..•••••••••••

11-12. Graphs showing:

11. Relation between c han g e s in stage of Tonto Creek and changes in water levels in wells (A-5-11)8bbc1 and (A-5-11)8bbc 2 .•..•••

12. Streamflow and c han g e s in water levels in wells .•.•• .00 ........ ".········

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19

22

24

25

CONTENTS

Figures 13-14. Maps showing:

13. Distribution and density of vegetation along the channel and flood plain of lower Tonto

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Page

Creek. . . . . . . . . . . . . . . . . . . . . . . . 29

14. Location 0 f wells and chemical quality of water along lower Tonto Creek • • • • • • • 35

TABLES

Table 1. Chemical analyses of water in the lower Tonto Creek basin .....•....•..............•..... 33

HYDROLOGIC REGIMEN OF LOWER TONTO CREEK BASIN, GlLA COUNTY, ARIZONA-A RECONNAISSANCE STUDY

By

H. H. Schumann and B. W. Thomsen

ABSTRACT

The 280-square-mile lower Tonto Creek basin is in the Central highlands water province of central Arizona. The basin is drained by Tonto Creek, which flows southward and discharges into Roosevelt Lake. The mountains that border the basinare composed chiefly of igneous and meta­morphic rocks, and the basin is underlain by more than 2,000 feet of uncon­solidated to semiconsolidated sedimentary deposits. The channel and flood plain of lower Tonto Creek are underlain by as much as 65 feet of alluvium.

In the lower Tonto Creek basin the principal sources of water are the precipitation, which ranges from 17 to more than 20 inches per year, and the streamflow that enters the area from the upper Tonto Creek basin. The precipitation that falls on the lower Tonto Creek basin produces about 20,000 acre-feet per year of streamflow. The streamflow that enters the lower basin from the 675-square-mile upper basin is measured at the north­ern end of the study area and averages about 80,000 acre-feet per year. An estimated 17,000 to 20,000 acre-feet of streamflow infiltrates annually into the highly permeable alluvium.

The alluvium is the principal aquifer in the lower Tonto Creek basin. Water levels in wells drilled in this aquifer rise quickly in direct response to floodflow in Tonto Creek, which indicates that a large part of the flow loss is recharged to the ground-water reservoir.

In the lower Tonto Creek basin water is discharged to Roosevelt Lake by streamflow and subsurface flow and to the atmosphere by evapo­transpiration. The flow from Tonto Creek that enters Roosevelt Lake av­erages about 80,000 acre-feet per year, the subsurface flow that enters the lake from the alluvium averages about 4,000 acre-feet per year, and the evapotranspiration losses average about 13,000 acre-feet per year.

1

2

Flow in Tonto Creek and ground water in the alluvium and the lower part of the basin fill are of excellent chemical quality and are suitable for most uses. The chemical quality of ground water in the alluvium and that of flow in Tonto Creek is similar because the alluvium receives most of its recharge from the creek. Water from a well drilled in the fine - grained facies of the upper part of the basin fill is unsuitable for drinking purposes.

INTRODUCTION

Purpose of the Investigation

The increasing demand for municipal, industrial, and irrigation water in the Salt River Valley in southern Arizona has created a need for an appraisal of the water resources of the watersheds above the storage reservoirs on the Salt River. The U. S. Geological Survey in cooperation with the Salt River Valley Water Users' Association conducted a hydrologic reconnaissance study in the lower Tonto Creek basin in the western part of Gila County, Ariz. (fig. 1), to obtain water-resources information for use in making water-management decisions. The investigation was made under the general supervision of H. M. Babcock, district chief of the U.S. Geo­logical Survey in Arizona.

Methods of the Investigation

All streamflow and precipitation records were analyzed to aid in the appraisal of the water resources of the area. The streamflow that enters the area from the upper basin is measured at the gaging station above Gun Creek, which has been in operation since 1941. A temporary streamflow­gaging station was installed on Tonto Creek above Greenback Creek to obtain a record of the low flows near the downstream end of the basin. In order to determine the amount of water lost to infiltration in lower Tonto Creek, re­petitive streamflow measurements were made at selected sites during pe­riods of base flow.

All wells in the area were inventoried, and the well locations were plotted, and the well locations are shown in figure 14 and are described in accordance with the well-numbering system used in Arizona, which is ex­plained and illustrated in figure 2. Three shallow observation wells were dug in the southern part of the basin as a part of this study. Periodic water­level measurements were made in s e I e c ted wells, and four wells were

36

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The well numbers used by the Geological Survey in Arizona are in accordance with the Bureau of Land Management's system of land subdivision. The land survey in Arizona is based on the Gila and Salt River meridian and base line, which divide the State into four quadrants. These quadrants are designated counterclockwise by the capital letters A, B, C, and D. All land north and east of the point of origin is in A quadrant, that north and west in B quadrant, that south and west in C quadrant, and that south and east in D quadrant. The first digit of a well number indicates the township, the second the range, and the third the section in which the well is situated. The lowercase letters a, b, c, and d after the section number indicate the well location within the section. The first letter denotes a particular l60-acre tract, the second the 40-acre tract, and the third the 10-acre tract. These letters also are as­signed ina counterclockwise direction, beginning in the northeast quarter. If the location is known within the 10-acre tract, three lowercase letters are shown in the well number. In the example shown, well number (A-4-5)19caa designates the well as being in the NEtNEtSWt sec. 19, T. 4 N., R. 5 E. Where more than one well is within a 10-acre tract, consecutive numbers beginning with 1 are added as suffixes.

FIGURE 2. --WELL-NUMBERING SYSTEM IN ARIZONA.

5

equipped with continuous water-level recorders to evaluate water-level changes in response to streamflow events in the lower Tonto Creek basin.

Water samples were collected from Tonto Creek and from selected wells for chemical analysis. The analyses were used to interpret the re­lation between streamflow and ground water. Reconnaissance geologic map­ping was done in order to determine the relation of the rock units to the control and availability of water. The density of natural vegetation and the distribution of cultivated acreage along the channel and flood plain of lower Tonto Creek were mapped on low-altitude aerial photographs to estimate evapotranspiration losses from the flood plain.

Location, Topography, and Drainage

The Tonto Creek basin occupies 955 square miles in the Central highlands province and is entirely in western Gila County (fig. 1). The lower Tonto Creek basin is defined as the drainage area from below the streamflow- gaging station, Tonto Creek above Gun Creek, to the high water­line of Roosevelt Lake (fig. 4)-an area of about 280 square miles. The area roughly corresponds to the area described by Feth and Hem (1963, p. 14) as the Tonto basin. The village of Punkin Center is near the center of the study area.

The basin is bounded on the west by the rugged Mazatzal Mountains and on the east by the Sierra Ancha, which rise sharply above the central basin. The south-sloping central basin has moderate relief and is dissected byTonto Creek and its tributaries. Several levels of stream-cut terraces are present along Tonto Creek in the northern part of the area. Altitudes range from about 2, 200 feet above mean sea level near Roosevelt Lake to more than 7, 100 feet in the Mazatzal Mountains.

Tonto Creek is an in t e r mit ten t stream that originates in the Mogollon Rim country northeast of Payson, Ariz., and flows southward into Roosevelt Lake (fig. 4). Lower Tonto Creek is about 17 miles long and has an average gradient of about 23 feet per mile.

Climate

The climate in the lower Tonto Creek basin is semiarid and is char­acterized byhot dry summers and mild winters. At the Reno Ranger Station near Punkin Center (fig. 4), the monthly mean temperatures range from

6

44.8°F in January to 86.2°F in July. The highest recorded temperature at this station was 115°F in July 1929, and the lowest recorded temperature was 10°F in January 1962 (Green and Sellers, 1964, p. 343).

The average annual precipitation ranges from about 17 inches in the lowest part of the basin near Roosevelt Lake to more than 20 inches in the mountains (Green and Sellers, 1964, p. 9). The average annual precip­itation is 18.73 inches for 35 years of record at the Reno Ranger Station (Green and Sellers, 1964, p. 343). The average annual precipitation at Roosevelt, which is about 10 miles south of the report area, is 13.62 inches for 1949-70 (V. S. Weather Bureau, issued annually).

Most of the precipitation occurs during the summer-July through September-and winter-December through March (fig. 3). The summer precipitation mainly is the result of high-intensity thunderstorms, which are of short duration and small areal extent. During the late summer, however, tropical storms from the Gulf of California or the Pacific Ocean may produce large amounts of precipitation over the basin and may result in large- scale flooding (Green and Sellers, 1964, p. 343). For example, the tropical storm of September 4-6, 1970, dropped morethan 11.0 inches of precipitation over the upper Tonto Creek basin, which caused the highest peak flows in the lower basin since possibly the early 1900's (Roeske, 1971, p. 11). The winter pre­cipitation is from frontal storms that move into the basin from the Pacific Ocean; these storms produce rainfall of low to moderate intensities at the lower altitudes and snowfall in the mountainous areas. Although slightly less than half the average annual precipitation occurs during the winter, winter precipitation produces most of the annual streamflow.

The average annual class A pan evaporation at Roosevelt for 1949-70 is 98.27 inches (V. S. Weather Bureau, issued annually). The average annual pan-evaporation rates are more than seven times greater than the average annual precipitation rates at this station (fig. 3).

ROCK VNITS AND THEIR WATER-BEARING PROPERTIES

The lower Tonto Creek basin is bounded on the east and west by rugged mountains that are composed chiefly of igneous and metamorphic rocks of Precambrian age (fig. 4). The south-sloping basin is underlain by morethan 2,000 feet of unconsolidated to semiconsolidated sedimentary deposits of Tertiary and Quaternary age.

The basin was formed during,Miocene and Pliocene time bylarge­scale faulting and uplift of the m 0 un t a in s that border the present basin

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EXPLANATION

AVERAGE MONTHLY PRECIPI-

\

2'

=

TATION AT ROO SEVELT, 1949-70; AVERA GE ANNUAL

IS 13.62 PRECIPITA TION INCHES

I AVERAGE MON THLY PAN

NAT 1949-70;

NUAL PAN N IS 98.27

EVAPORATIO ROOSEVELT, AVERAGE AN EVAPORATIO INCHES

MONTHLY POTE NTIAL PIRATION NO RANGER GTHE CRIDDLE D;ANNUAL VAPO-

EVAPOTRANS RATES AT RE STATION USIN BLANEY AND (1962) METHO POTENTIAL E TRANSPIRA TI ON IS 66.6 INCHES

\ "'" r---

'" ~",55

~ § ;;:: ~ ~~~

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

FIGURE 3. --AVERAGE MONTHLY PRECIPITATION, PAN EVAPORATION, AND POTENTIAL EVAPOTRANSPIRATION IN AND NEAR THE LOWER TONTO CREEK BASIN.

7

8

(Lance, 1960, p. 157). During and after the period of faulting, large quan­tities of material were eroded from the mountains and were deposited in the downfaulted central part of the basin.

Igneous and Metamorphic Rocks

Granite and related intrusive rocks are the main rock types ex­posed in the Mazatzal Mountains, which border the basin on the west; granite, diabase, and metamorphic rocks are the main rock types exposed in the Sierra Ancha, which border the basin on the east. These rocks are domi­nantlyof Precambrian age. The rocks along the northern part of the basin include schist and rhyolite of Precambrian age and basaltic lava flows of Tertiaryage, which crop out in a small area west of the Gun Creek gaging station.

The igneous and metamorphic rocks are relatively impermeable except where fractured or weathered. The fractured rocks and the weathered material, where more thana few feet thick, store a small amount of ground water, which is released slowly through small intermittent springs at the bases of the mountains. Because the igneous and metamorphic rocks are nearly impermeable and crop out in steep slopes, most of the precipitation that falls on the mountains results in overland flow.

Sedimentary Rocks

The basin is filled with more than 2,000 feet of unconsolidated to semiconsolidated sedimentary deposits of Tertiary and Quaternary age, which comprise the undifferentiated upper and lower parts of the basin fill, unmapped piedmont and terrace gravels, and alluvium. The lower part of the basin fill is exposed along Slate and Tonto Creeks in the northwestern part of the area, and the upper part of the basin fill underlies the central part of the area. The basin fill is overlain by thin layers of piedmont gravel of Quaternary age along the slopes of the basin.

The thin discontinuous layers of piedmont gravel extend from the bases of the mountains to the flood plains of Tonto Creek and its major trib­utaries. The piedmont g r a vel consists of poorly sorted unconsolidated reddish-brown gravel, sand, silt, and clay. Although the material is moder­ately permeable, it is cut by several washes and generally occurs above the regional water table; therefore, the piedmont gravel does not store large amounts of water.

BASE FROM U. S. GEOLOGICAL SURVEY, 1:125, 000 ROOSEVELT, 1912; 1:62,500 PAYSON, 1936 AND DIAMOND BUTTE, 1937

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1

I 2

I 3

I 4

I 5 MILES I

EXPLANATION

ALLUVIUM UNCONSOLIDATED SAND AND GRAVEL AND SMALL AMOUNTS

OF SILT AND CLAY; HIGH PERMEABILITY; YIELDS LARGE AMOUNTS OF WATER TO WELLS

fjJ!i%I~J!Jill BASIN FILL, UNDIFFERENTlA TED

DIVIDED INTO TWO PARTS. THE UPPER PART CONSISTS OF A COARSE-GRAINED FACIES AND A FINE-GRAINED FACIES; LOW PERMEABILITY. THE LOWER PART CONSISTS OF UN­CONSOLIDATED TO SEMICQNSOLIDATED INTERBEDDED GRAVEL, SAND, AND SANDSTONE; LOW TO MODERATE PERMEABILITY; YIELDS SMALL AMOUNTS OF WATER TO WELLS

IGNEOUS AND METAMORPHIC ROCKS CONSIST MAINLY OF GRANITE AND RELATED INTRUSIVE ROCKS

IN THE MAZATZAL MOUNTAINS; GRANITE, DIABASE, AND ¥ETAMORPHIC ROCKS IN THE SIERRA ANCHA; AND SCHIST AND RHYOLITE IN THE NORTHERN PART OF THE BASIN (INCLUDES OUTCROPS OF BASALTIC LAVA FLOWS OF TERTIARY AGE IN A SMALL AREA WEST OF THE GUN CREEK GAGING STATION). GENERALLY VERY LOW PERMEABILITY; LOW TO MODERATE PERMEABILITY WHERE FRACTURED AND IN WEATHERED ZONES

CONTACT DASHED WHERE APPROXIMA TE

DRAINAGE DIVIDE

A STREAMFLOW-GAGING STATION

(OPERATED BY THE U. S. GEOLOGICAL SURVEY)

GEOLOGY MODIFIED FROM WILSON, MOORE, AND PEIRCE (1959) BY H. H. SCHUMANN (1970)

FIGURE 4. --GENERALIZED GEOLOGIC MAP OF THE LOWER TONTO CREEK BASIN

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Thin discontinuous ribbons of terrace gravel of Quaternary age cap the terraces, which crudely parallel the present course of Tonto Creek, and grade into the piedmont graveL These terraces are well developed north of Punkin Center. The terrace gravel consists of poorly sorted light- brown to gray sand, gravel, silt, and clay and is generally less than 20 feet thick. Although the terrace gravel is highly permeable, it is of limited areal extent and generally occurs above the water table.

Basin Fill

The basin fill is divided informally into hvo parts-a lower part and an upper part. The boundary between the lower and upper parts of the basin fill is exposed only along streambanks and is not delineated on the map. The reddish-gray coarse-grained lower part of the basin fill overlies the Precambrian schist and is exposed along lower Slate Creek and Tonto Creek above Slate Creek. The lower part of the basin fill consists of unconsolidated to semiconsolidated interbedded gravel, sand, and sandstone. The gravel beds are poorly sorted and contain silt and sand and are weakly cemented with calcium carbonate. The sand and sandstone beds are poorly sorted and commonly contain pebbles.

The lower part of the basin fill un con for m a b I Y overlies the Precambrian schist and is tilted basinward where it is exposed along lower Slate Creek; there, the lower part of the basin fill contains interbedded basaltic lava flows and is overlain by the upper part and by alluvium along stream channels. Becausethe overlying upper part of the basin fill contains fossils of Pliocene age, a Pliocene or older age is assigned to the lower part (Lance, Downey, and Alford, 1962).

The cementation and poor sorting of the lower part of the basin fill effectively reduce the size of the pore spaces and the degree of intercon­nection between them; therefore, the permeability of the lower part is low to moderate. The lower part of the basin fill yields small quantities of water to wells in the northern part of the basin. The lower part of the basin fill is capable of yielding small to moderate quantities of water suitable for stock and domestic supplies if a sufficient saturated thickness of the material is penetrated.

The upper part of the basin fill unconformably overlies the lower part and laps onto the Precambrian rocks of the adjacent mountains (fig. 4). The upper part of the basin fill is overlain by thin layers of piedmont gravel along the bases of the mountains and by thin terrace gravel and alluvium in the channels of Tonto Creek and its major tributaries. The upper part of

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the basin fill is exposed along the east and west sides of the basin and con­sists of a coarse-grained and a fine-grained facies,

The coarse - grained facies crops out in a narrow band along the margins of the basin and consists of light-gray to brown poorly consolidated gravel layers interbedded with silty to gravelly sand. The coarse- grained facies is of 1 i mit e d areal extent and grades into the fine- grained facies toward the center of the basin. The coarse - grained facies overlies the Precambrian schist and the lower part of the basin fill in exposures in the north-central part of the basin. The coarse-grained facies is moderately permeable; however, because the facies is cut by large washes and generally is above the water table, it is not an important aquifer.

The fine- grained facies consists chiefly of red to gray thin- to very thick-bedded poorly consolidated silt and clay and minor amounts of inter­bedded sand, gypsum, marl, and tuff. Many gypsiferous red beds are ex­posed in the southern part of the area but thin northward and are not present in the central part of the basin. A thin fossiliferous light-brown silt, clay, tuff, and marl sequence 0 v e r 1 i e s the gypsiferous red beds near Punkin Center. The animal and plant remains in this sequence are of Pliocene age and probably were buried by deposits of a large lake (Lance, Downey, and Alford, 1962).

Most of the upper part of the basin fill is rather impermeable, al­though thin sand layers intercalated with the silt and clay yield small amounts of water of poor quality to wells near Punkin Center. These beds are a con­fining layer for underlying water- bearing beds, and also inhibit infiltration of water from the overlying unconsolidated alluvium a 1 0 n g Tonto Creek (fig. 4).

Alluvium

Unconsolidated alluvium of Quaternary age is present in a contin­uous strip along the channel and flood plain of Tonto Creek and along the lower parts of its major tributaries (fig. 4). The alluvium consists of light­brown to gray sand and gravel and small amounts of silt and clay. The allu­vium overlies the Precambrian schist at the gaging station on Tonto Creek above Gun Creek; it is as much as 65 feet thick where it overlies and is in hydraulic connection with the lower part of the basin fill between the gaging station and Punkin Center (fig. 4). The alluvium is 30 to 40 feet thick where it overlies the upper part of the basin fill along lower Tonto Creek in the southern part of the area.

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The alluvium occupies the lowest topographic position in the basin and receives water from adjacent units and from Tonto Creek; the unit re­ceives water from and discharges it to the creek depending on the stage of the stream. The highly permeable alluvium is the principal aquifer in the basin and yields as much as 2,500 gpm (gallons per minute) of waterto large­diameter irrigation wells. Many small-diameter domestic and stock wells obtain their water from this unit.

HYDROLOGY

The Central highlands province, of which the lower Tonto Creek basin is a part, receives the largest amount of precipitation of any of the water provinces in Arizona. The runoff from most of the province is stored in the reservoirs on the Salt River to provide water and hydroelectric power for irrigation, municipal, and industrial uses in the arid Salt River Valley. Tonto Creek drains into Roosevelt Lake, which is the oldest and largest of the reservoirs on the Salt River.

The hydrologic system of the lower Tonto Creek basin is shown diagrammatically in figure 5. Water en t e r s the lower basin chiefly as streamflow from the upper basin and as precipitation. Water that enters the lower basin as precipitation may evaporate soon after contact with the land surface, move across the land surface as runoff, or infiltrate into the earth to become either soil moisture or ground water. Water that moves across the land surface tends to collect and become streamflow. As stream­flow moves along natural channels, some water evaporates, and some infil­trates into the streambed and becomes either soil moisture or ground water.

The precipitation or streamflow that infiltrates into the earth and that is retained in the unsaturated zone above the water table is called soil moisture and may be removed by evaporation and by transpiration through plants. Water that reaches the water table becomes ground water and moves through the earth very slowly from areas of greater hydraulic head to areas of lesser hydraulic head. Ground water may return to the land surface and become streamflow where the water table intersects the streambed, it may move upward into the unsaturated zone and become soil moisture, or it may be removed by evaporation and transpiration.

Water leaves the basin as streamflow and ground-water discharge to Roosevelt Lake and by evaporation and transpiration (fig. 5). The com­bined discharge of water to the atmosphere by evaporation and transpiration is termed" evapotranspiration .••

;/~~' . Streamflow- gaging station

abo;'e Gun Creek .. '

Precambrian rocks, . chiefly gneiss and schist

Precipitation

i Streamflow and underflow

from tributaries

Water lost through'" transpiration

Upper part of the basin fill

Water lost through evaporation

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..... "'"

St""eamflow to Roosevelt Lake

table

• Note: Direction of ground­

water flow

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FIGURE 5. --HYDROLOGIC SYSTEM IN THE LOWER TONTO CREEK BASIN.

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15

Streamflow

Most of the streamflow in lower Tonto Creek originates in the upper basin, which has a drainage area of 675 square miles. The flow from the upper basin is measured at the gaging station above Gun Creek and ranged from 17,120 acre-feet in 1956 to 224,500 acre-feet in 1952 (fig. 6). The average annual streamflow for the period 1942-70 was 110 cfs (cubic feet per second) or 79,700 acre-feet per year (U. S. Geological Survey, 1970). Most of the streamflow occurs in the winter and spring-morethan 75 per­cent occurs from December through May-and the lowest flows occur in June (fig. 7). The peak flow was 53,000 cfs on September 5, 1970, and periods of no flow are uncommon.

The time distribution of streamflow may be expressed by a flow­duration curve, which is a cumulative frequency curve that shows the per­centage of time that specified discharges are equaled or exceeded in a given period without regard to the sequence of occurrence. For example, the curve in figure 8 does not show whether the lowest flows occurred consecu­tively in a rare drought year or whether low flows occurred on a few days during each year. Tonto Creek fiows on the average of 97.4 percent of the time, and a discharge of 20 cfs is equaled or exceeded 50 percent of the time (fig. 8).

Low Flows

Streamflow from the upper Tonto Creek basin is the only source of sustained flow in the lower basin. In 13 years of the 29 water years of record, 1942-70, short periods of no flow were recorded at the gaging sta­tion above Gun Creek. The periods of no flow usually occur in June and July, and the longest period of no flow was 40 days recorded in 1956.

Low - flow frequency curves are based on the 10,west mean dis­charges for intervals of time ranging from 1 to 183 pqnsecutive days for each year of record and give recurrence intervals, rnagiiltudes, and the chrono­logical sequences of the occurrence of the low flows. The low-flow frequency curves in figure 9 show that a 30~day mean flow of 0.1 cfs has an expected recurrence interval of about 6 years at the gaging station above Gun Creek.

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Maximum flow ~ 22~ 500 acre-feet

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o c­O> ..-<

~

FIGURE 6. --ANNUAL FLOW OF TONTO CREEK ABOVE GUN CREEK, NEAR ROOSEVELT, ARIZ., 1942-70 WATER YEARS.

~

0>

17

20 -

18 -

16 -

14 -

12 -

10 -

8 -

6 -

4 -

2 -I

o I

oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

FIGURE 7. --AVERAGE MONTHLY FLOW OF TONTO CREEK ABOVE GUN CREEK, NEAR ROOSEVELT, ARIZ., 1942-70 WATER YEARS.

18

200 0

100 0

I-----

-

-

-

100 ---

--

-

-

-

10 f--I-I-I-

I-

I-

I-

I-

f--I-I-I-

f--

I-

I-

f--

O. 1 0,01

1\ If 1\ \ -

-

1\ --

-

-

\ -

-

1\ \ -

--

\ --

-

\ -

\ -\

\ 1\ -

--

1\ -

-

-

-

1\ -

\ ----

-

-

-

-

0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

FIGURE 8. --FLOW-DURATION CURVE FOR TONTO CREEK ABOVE GUN CREEK, NEAR ROOSEVELT, ARIZ., 1942-70 WATER YEARS.

19

J83 'clqy

J <0 ~ell.1:J 0

'clqy Z ~eql:J 0 10 U fxl fJO,cI. [f)

0:: qy~

fxl eqiJ A. 6'0 t-< '<Ill.;. fxl fxl <q() r:.. ll~

U <.90 ..... >Q , ;:J 9Q u u.

ts ~o ~.q

rz:f 1 CJ 0::

~ U [f) H

0

RECURRENCE INTERVAL, IN YEARS

FIGURE 9. --LOW-FLOW FREQUENCY CURVES FOR TONTO CREEK ABOVE GUN CREEK, NEAR ROOSEVELT, ARIZ.

20

Tributary Flows

The tributaries to Tonto Creek flow only for short periods mainly in response to runoff from precipitation, Although the tributary flows are not measured, it is estimated that about 20,000 acre-feet per year of trib­utary streamflow reaches Roosevelt Lake, This estimate is based on the average unit discharge from similar nearby watersheds for which long-term runoff records are available.

Infiltration of Streamflow

The channel of lower Tonto Creek is about 500 feet wide and is underlain by the permeable alluvium. The streamflow that passes the gaging station above Gun Creek usually diminishes in the downstream direction as water infiltrates into the alluvium, and the lower reaches are often dry dur­ing the summer months. The average annual volume of infiltration for the period 1942-70 was estimated to be about 20,000 acre-feet or about 25 per­cent of the streamflow that passed the Tonto Creek above Gun Creek gaging station. The estimate is based on the infiltration-duration relation derived from the flow - duration curve for Tonto Creek above Gun Creek and from the average relation between rates of inflow and infiltration (Burkham, 1970). The instantaneous infiltration rates were computed as the difference between instantaneous rates of inflow and outflow measured when the flow in Tonto Creek was fairly constant and when there was no known tributary inflow; the computation was bas e d on the assumption that the aquifer was not com­pletely saturated, which was not true at all times or in all places. There­fore, the actual average annual volume of infiltration probably is less than the estimated annual volume of 20,000 acre-feet. An estimate of 17,000 acre-feet maybe c1oserto the actual average annual volume of infiltration along lower Tonto Creek based on the combined estimated annual volumes of subsurface outflow and evapotranspiration. The amount of tributary flow that infiltrates into the alluvium is unknown.

Flow to Roosevelt Lake

The average annual volume of streamflow that enters Roosevelt Lake from Tonto Creek is estimated to be 80,000 acre-feet per year. This estimate is based on the relation between unit discharge and watershed size for the data-collection sites on Tonto Creek,

21

Ground Water

Occurrence and Movement

In the lower Tonto Creek basin most of the ground water is stored in the sedimentary rocks that underlie the central part of the basin (fig. 4). Small amounts of ground water are stored in the igneous and metamorphic rocks where they are fractured or weathered; the fractured rocks and the weathered material, where more than a few feet thick, release the water slowly through small intermittent springs at the bases of the mountains.

In the north - central part of the basin and elsewhere along Tonto Creek the ground water is under unconfined conditions in the lower part of the basin fill where it is overlain by and hydraulically connected with the alluvium. In the south-central part of the basin ground water is under con­fined conditions in the lower part of the basin fill where it is overlain by the relatively impermeable fine - grained facies of the upper part of the basin fill. Ground water is under water - table conditions in the alluvium along lower Tonto Creek and its major tributaries; where the piedmont and ter­race gravel is saturated, the shallow ground water is under water-table con­ditions.

Ground water moves from areas of greater hydraulic head to areas of lesser hydraulic head. Water levels in wells drilled in the basin fill indi­catethat ground water moves from the sides of the basin toward lower Tonto Creek.

The principal direction of ground-water movement in the alluvium is southward to Roosevelt Lake. Lower Tonto Creek is a losing stream where the altitude of the water table is below the altitude of the streambed, and the ground water moves laterally in the alluvium away from the creek (fig. lOA). Lower Tonto Creek is a gaining stream where the altitude of the water table is above the altitude of the streambed, and ground water moves laterally in the alluvium toward the creek (fig. lOB).

Recharge

The ground - water reservoir in the lower Tonto Creek basin re­ceives recharge from infiltration of streamflow and irrigation water. Most of the recharge to the ground - water reservoir is from the infiltration of streamflow.

22

A

LOSING REACH

..... ' Tonto Creek

B GAINING REACH

~~'=--- ----

.:.,;,.'.'./-- -- -- --

Basin fill

EX PLA NA TION

WATER TABLE

~

DIRECTION OF

GROUND-WATER FLOW

FIGURE 10. --GAINING AND LOSING REACHES OF LOWER TONTO CREEK.

23

Infiltration of streamflow. --Water-level and chemical data indi­cate that the ground water in the alluvium is associated closely with the flow in lower Tonto Creek. Water levels in two shallow observation wells drilled in the alluvium near the gaging station Tonto Creek above Greenback Creek fluctuate in response to changes in stage of Tonto Creek (fig. 11), which in­dicates a hydraulic interconnection between the stream and the ground water in the alluvium.

Hydrographs of water levels in observation wells drilled in the allu­vium along Tonto Creek and streamflow at the Tonto Creek above Gun Creek gaging station show general rises in water levels in the early spring in re­sponse to winter runoff and declines in the spring and early summer; a second series of rises in water levels occurs during the summer and fall in response to late summer flows (fig. 12). The water-level rises indicate that a large part of the streamflow that disappears from the channel infil­trates into the alluvium and becomes ground water.

In the few wells that penetrate the basin fill east of Tonto Creek water-level measurements indicate that water moves downgradient toward the creek in this unit. Therefore, infiltration of the intermittent stream­flow that originates in the adjacent mountains contributes an undetermined amount of recharge to the ground-water reservoir.

Infiltration of precipitation and irrigation water .- -Direct precipi­tation on the lower Tonto Creek basin probably is not a significant source of recharge to the ground - water reservoir. The low permeability of the upper part of the basin fill precludes penetration of precipitation to the water table, and much of the precipitation is lost directly to the atmosphere be­cause of the high evaporation rates. The amount of recharge to the alluvium from direct precipitation probably is small because of interception losses to plant cover, soil-moisture deficiencies during much of the year, and the limited areal extent of this unit.

Some of the irrigation water applied on the flood plain probably re­turns to the aquifer; however, return of irrigation water pumped from the alluvium is a recycling process and does not constitute recharge of new water to the aquifer. The amount of irrigation water recycled tothe aquifer is small because the irrigated area includes only about 350 acres.

f:<l U

~ 5 Il:i P rJ.l

~

j ::: 6

3 Water level in well f:<l P=l (A-5-11)8bbc 1, Eo< 150 feet west of gage f:<l f:<l 7 Ii<

~ 6 • Il:i

f:<l Eo<

~ ~ 7

~ Water level in well A. f:<l (A-5-11)8bbc2' ~ 300 feet west of gage

8

February 1970 March 1970

FIGURE 11. --RELATION BETWEEN CHANGES IN STAGE OF TONTO CREEK AND CHANGES IN WATER LEVELS IN WELLS (A-5-11)8bbc1 AND (A-5-11)8bbc2'

'"

,

,0'

.. " " " "

~ , ~

J , , I

Well CA-S-IO)U .. b ..

~ Well {A-~-1I)Sbbc2

"

\ ~ , , ,

" ' .. -\

25

, h ,,,,/1\ "J ~ , 'v)J -A , , , I

, , , , I ' , I

FWW OF T01.'Q CREEK ABOVE OlIN CREEK, NEAl! ROOSEVELT

l E • 1 \/\--j

f < I

: 10 '-\ l'\... ...... --.-_ .............. '.---, " " -- ~P"~T_ -; 11 .... ---. __ ..

e " " ............. ,., / '.. ,/ :yEASURED~ATER LRVl:L : .... -\ /", / '-'""...... -... , ... Well (A-5-1I}Sbdc -... " 5 13 ~ ............. / __ /

o "+---r--''--C---'--'---'--'---C--'---r---'--'---r--'---.--'---'--'---r--,,--,2e'r.L,---.--,--~.p~n~oX~""~T~'~W~A~T'~'~'~'~V'~'c--+ I I I I I I I I I I I I I , I I I I I I I I I I I I I I I I

RECORDED WATEf! LEVEL

WATER LEVEt.S IN WELUI

FIGURE 12. --STREAMFLOW AND CHANGES IN WATER LEVELS IN WELLS.

26

Discharge

About 17, 000 acre-feet per year of water is discharged from the ground-water reservoir in the lower Tonto Creek basin-about 4,000 acre­feet by subsurface flow to Roosevelt Lake and about 13,000 acre-feet by evapotranspiration. Ground water also is discharged by subsurface flow to Tonto Creek and by pumping from wells. Small amounts of water are pumped from many small-diameter wells for livestock and domestic uses; a few irrigation wells yield large amounts of water, but the am 0 u n t of water pumped from these wells does not constitute a large draft on the ground­water reservoir at the present time. Water discharged from the ground­water reservoir by evapotranspiration is discussed separately in the section entitled "Water Losses by Evapotranspiration." The amount of ground water discharged to Tonto Creek is unknown and is dependent on the altitude of the water table in relation to the altitude of the streambed (fig. 10).

The amount of ground water discharged to Roosevelt Lake from the alluvium along lower Tonto Creek can be computed using an equation based onDarcy's law (Wenzel, 1942, p. 3); the terminology and units of measure­ments have been changed to conform to the current usage of the U.S. Geo­logical Survey (Lohman and others, 1972). The equation is

Q = TIW, (1)

where

Q = discharge, in cubic feet per day, T = transmissivity, in cubic feet per day

per foot, I = hydraulic gradient, in feet per foot,

and W = average width of flow channel, in feet.

The transmissivity of the all u vi u m can be estimated using the expression

where

T = bK,

b = saturated thickness, in feet, and K = average hydraulic conductivity, in

feet per day.

(2)

27

The term' 'hydraulic conductivity" of an aquifer material replaces the term "field coefficient of permeability. " Based on field determinations of the coefficient of permeability of a similar aquifer in the adjacent Syca­more Creek watershed (Thomsen and Schumann, 1968, p. 39) and on labora­tory studies of unconsolidated sand and gravel (Todd, 1959, p. 53), the hy­draulic conductivity of the alluvium is estimated to be 700 feet per day. If the average saturated thickness of the unit is about 40 feet, the transmis­sivity is estimated to be 28,000 cubic feet per day per fooL The aquifer is about 4,800 feet wide immediately downstream from the confluence of Tonto and Greenback Creeks and the hydraulic gradient is about 18.5 feet per mile. Using equation (1), the subsurface discharge to Hoosevelt Lake through the alluvium along lower Tonto Creek is estimated to be

Q = (28,000)(18.5/5,280)(4,800) = 4.7 x 105 cubic feet per day = about 4,000 acre-feet per year.

Some water is discharged to Hoosevelt Lake from the basin de­posits. However, sufficient subsurface geologic data are not available to estimate the amount of discharge from this unit.

Water Losses by Evapotranspiration

Water is discharged to the atmosphere by evaporation of surface water, by evaporation of soil moisture, and by direct evaporation of ground water where the water table is near the land surface. Water also is dis­charged to the atmosphere by transpiration through plants that use the soil moisture above the water table and through plants that have deep roots that tap the ground-water reservoir. The long-term net change in soil moisture is assumed to be zero in the lower Tonto Creek basin.

A plant that habitually obtains its water supply from ground water is called a phreatophyte (Meinzer, 1923, p. 55). Transpiration by natural and cultivated phreatophytes accounts for most of the water lost byevapo­transpiration in the basin. The phreatophytes in the areas of shallow ground water along the channel of lower Tonto Creek and its flood plain consist mainly of mesquite, cottonwood, and saltcedar; the alfalfa that is cultivated on the flood plain also is considered a phreatophyte.

28

The channel and flood plain of lower Tonto Creek have an area of about 5,080 acres; the distribution and density of vegetation along the channel and flood plain are shown in figure 13. In August 1967 about 350 acres or 7 percent of the area was under cultivation. Dense growths of phreatophytes covered about 865 acres or 17 percent of the area, and growths of phreato­phytes of light to medium densities covered 2,700 acres or 53 percent of the area. Relatively clear areas having very little phreatophyte growth covered 1, 160 acres or about 23 percent of the area.

Potential Evapotranspiration

Potential evapotranspiration is defined as the water loss that will occur if at notimethere is a deficiency of water in the soil for use byplants (Langbein and Iseri, 1960, p. 15). If it is assumed that potential evapo­transpiration is about equal to lake evaporation, the potential evapotranspi­ration rate can be estimated using the available pan-evaporation data (Cruff and Thompson, 1967, p. 19). Therefore, the average annual potential evapo­transpiration rate in the stu d y area is about equal to the average annual class A pan-evaporation rate of 98.27 inches at Roosevelt (U. S. Weather Bureau, issued annually) times 0.7, which is the ratio of lake evaporation to class A pan evaporation, or about 69 inches per year.

The Blaney and Criddle (1962) method of estimating potential evapotranspiration is based on temperature, daytime hours, and available moisture for different crops (Cruff and Thompson, 1967, p. 15). Using these parameters, potential evapotranspiration can be computed by the equation

where

U = KI: (T)(p) 100

U = consumptive use, in inches, during the growing season,

K = empirical consumptive - use coeffi­cient that is dependent primarily on the type of vegetation,

p = monthly percentage of total daytime hours in the year, and

T = mean monthly temperature, in de­grees Fahrenheit.

(3)

I

I

I

34°00'----

T.

8 N.

T.

BASE FROM U. S. GEOLOGICAL SURVEY. 1:24.000 GREENBACK CREEK. 1964; KAYLER BUTTE. 1964~

PICTURE MOUNTAIN. 1964: TONTO BASlN. 1964.

l'iBt4

36

6

Sycamore

.,~

EXPLANATION

-AREA UNDER CULTIVATIotl

D CLEAR AREA. VERY LITTLE

VEGETATION

LICHT TO MEDIUM VEGETATION DENSITY

-DENSE VEGETATION

T. 6 N.

T. L ______________ +_"----+- I I 5

o 2 3 4 MILES 1 I I I

N.

VEGETATION MAPPED ON AERIAL if'!JW'l'OORA.iPJoIS FOR 1967 BY H. H. SCHU'JofANN

FIGURE 13. --DISTRIBUTION AND DENSITY OF VEGETATION ALONG THE CHANNEL AND FLOOD PLAIN OF LOWER TONTO CREEK. "" <Ii>

31

The monthly potential evapotranspiration rates forthe lower Tonto Creek basin computed by the Blaney and Criddle method using a value for K of 1.0 are shown in figure 3. The annual potential evapotranspiration rate is 66.6 inches or 5.55 feet, which is within 4 percent of the potential evapo­transpiration value computed from pan evaporation.

Evapotranspiration Losses

Evapotranspiration losses can be estimated from potential evapo­transpiration rates if the type of vegetation and the depth to water are known. Blaney suggested a value for K of O. 85 for the entire year for estimating evapotranspiration losses from an alfalfa field (Cruff and Thompson, 1967, p. 16). Other investigators have suggested values for K that are dependent not only on the type of phreatophyte but also on the average depth to the water table (Rantz, 1968, p. 11). Using the suggested values of K, estimates of annual evapotranspiration losses were computed by the equation

where

Q = (U)(K)(D)(A),

Q = evapotranspiration loss, in acre-feet. U = potential evapotranspiration los s, in

feet, K = empirical consumptive-use coefficient

that is dependent mainly on type of vegetation,

D = factor by which to multiply K value for density of growth, and

A = area of phreatophytes by densityc1ass, in acres ..

(4)

Using the equation for cult i vat e d alfalfa and den s e phreatophytes,

Q = (5.55)(0.85)(1.00)(1,215) = 5,700 acre-feet.

Using the equation for light to medium phreatophyte density,

Q = (5.55)(0.60)(0.75)(2,700) = 6,700 acre-feet.

Therefore, the water used by phreatophytes is calculated to be about 12,400 acre-feet.

32

Evaporation losses from the clear areas, which have very little phreatophyte growth and an estimated average depth to water of 5 feet, were computed from pan- evaporation data (Todd, 1959, p. 156). The clear area of 1,160 acres was multiplied by 5 percent of the average annual pan­evaporation rate of 98.27 inches at Roosevelt, which gives an estimated average annual evaporation loss of 500 acre-feet.

The total ann u a 1 evapotranspiration loss from the lower Tonto Creek basin is estimated to be 13,000 acre-feet. The average annual evapo­transpiration loss per acre is estimated to be 2.6 acre-feet.

Chemical Quality of Water

Water samples were collected from lower Tonto Creek and from selected wells for chemical analysis (table 1). The similarity between the chemical composition of the streamflow and that of the ground water in the alluvium indicates that this aquifer receives most of its recharge by infil­tration of streamflow from lower Tonto Creek. The chemical composition of water at selected sites along Tonto Creek is shown graphically in figure 14.

The water from Tonto Creek is of excellent chemical quality and is suitable for most uses. The dissolved-solids concentrations in the water sampled on May 25, 1970, ranged from 255 to 274 mg/l (milligrams per liter); hardness, as calcium carbonate, ranged from 157 to 185 mg/l, and the water is classified as hard to very hard. Fluoride concentrations ranged from 0.3to 0.5 mg/l, and the main constituents were calcium and bicarbonate (fig. H), The samples were collected during a period of base flow and prob­ably represent the near maximum concentrations of dissolved solids that maybe expected in the flow of lower Tonto Creek. The chemical composition of the water samples collected in 1970 is very similar to that of the samples collected in 1952 (table 1).

Water samples from shallow wells drilled in the alluvium along Tonto Creek also were of excellent quality and the chemical composition is very similar to that of the samples collected from the creek. Dissolved­solids concentrations ranged from 235 to 402 mg/l, and hardness, as cal­cium carbonate, ranged from 211 to 238 mg/l. Fluoride concentrations ranged from 0.3 to 0.5 mg/l, and the main ionic constituents were calcium and bicarbonate (fig. 14).

Water from well (A-7-10)13bba, which is in the northern part of the basin and obtains its water from the lower part of the basin fill, is a

Table 1. --Chemical analyses of water in the lower ToDto Creek busin

[Results in milligrams per liter, except a.s indicated. Remarks: 5, sample obtained from atrerunflow; W, sample obtained from well)

Hardness Specific

D:la8olved as CaC03 conduct-Dat, Silica Calcium Magne- Sodium and Bicar- Car~

Sulfate Chlo- Fluo-solids Cal- Non-

Location 'f Bium potassium bonate bonate rid, ride cium, ""'" (Si02) (Ca) (SO'll (calcu- .=- (micro-collection (Mg) (Na + K) (He°a ) (COa' (CI) (F) lated) magne- bon- mhos at sium at, 2S·C)

(A-5-11)8bb 5-25~70 18 42 14 30 16S 0 40 34 0.5 261 163 26 490

8bbcl 5-25-70 IS 36 33 24 22S 0 40 34 .5 298 225 3S 530

8bbc2 5-25-70 18 71 14 8 258 0 30 22 .4 300 236 25 560

S. 10-2a-52 20 64 16 24 20S ---- 62 30 .4 31S 226 ---- 520

(A-6-10)2baa 5-25-70 15 51 14 25 193 0 14 47 .3 261 185 27 475

10dad 1 1-23-70 ------- 156 50 1,010 ---~-- ---- 2,700 24 3.0 3,940 600 ---- -----10dad2 8-27-70 18 71 11 36 254 0 24 32 .4 307 221 ---- 550

llcdb 5-25-70 15 50 13 25 193 0 15 42 .3 255 179 21 455

llcdd 8_27_70 17 47 12 46 170 4 15 54 .4 263 165 ---- 490

14aba2 8_27_70 9.1 47 13 38 184 0 11 40 • 3 235 169 ---- 459

14abdl 8_27_70 11 57 17 26 230 0 11 41 .3 276 212 ---- 525

14bbd 8-27-70 30 61 21 51 252 0 79 36 .3 402 23S ---- 698

26aba2 5-25-70 17 SO 15 26 226 0 34 32 .4 295 211 26 510

36abc 5-25~70 16 54 12 25 195 0 27 33 .3 263 182 22 450

(A-7-10)2acc 5-25-70 14 41 13 42 174 0 13 65 .4 274 157 14 SOO

10. 10-16-52 16 48 13 27 196 ---- 13 40 .4 254 174 ---- 449

Ilbcd 5-25-70 16 65 17 37 276 0 15 48 .3 334 230 4 605

13bba. 5-25-70 29 64 28 34 281 0 16 72 .2 381 274 44 680

15dda 5-25-70 14 SO 14 28 187 0 14 53 .3 265 182 29 490

'-...------ --- ___ L. ____ . _____ - - - -

pH

7.7

7.8

7.6

---7.S

---7.9

7.9

S.3

7.4

7.8

S.l

8.0

8.2

7.9

---7.7

7.9

8.0

Remarks

S.

W.

W.

S.

S.

W; arsenic, 0.21.

W.

S.

S.

W .

W.

W.

W.

S.

S.

S.

W.

W.

S.

'" '"

34

calcium magnesium bicarbonate type and is similar in chemical composition to ground water in the alluvium and to water in Tonto Creek (fig. 14); how­ever, the water has a slightly higher dissolved-solids content and hardness. The fluoride content of the water from this well was 0.2 mg/l. The chemical quality of the water from this well probably is indicative of that in the lower part of the basin fill in the northern part of the basin.

Well (A-6-10)10dad1 was drilled to a depth of 207 feet in the fine­grained facies of the upper part of the basin fill near Punkin Center in the central part of the basin. The water sample from this well contained 3,940 mg/l dissolved solids and the hardness was 600 mg/l; the fluoride concen­tration was 3.0 mg/l. The main ionic constituents were sodium and sulfate, which is in sharp contrast to the calcium bicarbonate water in the alluvium and in Tonto Creek. The water from well (A-6-10)10dad1 is undesirable for most uses owing to the large amount of dissolved solids and the large fluoride content. The arsenic content of 0.21mg/l is morethanfourtimestheman­datoryrejection limit of 0.05 mg/l for drinking water (U. S. Public Health Service, 1962). Water of similar chemical composition may be present in the fine- grained facies of the upper part of the basin fill in the central and southern parts of the basin.

The similarity in the chemical composition of streamflow in Tonto Creek and of ground water in the alluvium is indicated by the size and shape of the diagrams in figure 14. On May 25, 1970, the dissolved-solids content of the ground water from the alluvium was slightly higher than that of the water in Tonto Creek (table 1). The difference probably was due to a slight concentration of the dissolved solids inthe ground water as a result of evapo­transpiration ..

SUMMARY AND CONCLUSIONS

Water enters the lower Tonto Creek basin mainly as streamflow from the upper basin and as precipitation. The streamflow that enters the lower basin is measured at the Tonto Creek above Gun Creek gaging station and averages about 80,000 acre-feet per year. The streamflow that origi­nates in the lower basin in response to the annual precipitation of 17 to more than 20 inches contributes about 20,000 acre-feet per year of surface water to Roosevelt Lake. Part of the streamflow infiltrates into the highly perm­eable alluvium that underlies Tonto Creek and its flood plain. Water levels in wells drilled in the alluvium rise in direct response to floodflow in the creek, which indicates that a large part of the water lost as streamflow in­filtrates to recharge the ground-water reservoir.

MAGNl!:lSIVM (.lI4gl

T. 8 N.

o

T.

I I I I I I ~------~~~~~~--

7 .~_~.:--:: .• e -,

)~;'----

• ...--~ °0 0

3000 0 00 'b

o 00 00

INSET

o MILE , o 5000 FEET I I

a_ ' BASE FROM U.S: GEOLOGICAL SURVEY, 1:24.,000 GREENBACK CREEK, 1964~ KAYLER BUTTE, 1884; PICTURE MOUNTAIN. 1964; TONTO BASIN. 1964

o 2 3 4 MILES GEOLOGY BY H. H. SC1ruMANN, 1970 J I [ !

FIGURE 14. --LOCATION OF WELLS AND CHEMICAL QUALITY OF WATER ALONG LOWER TONTO CREEK. '" c.n

37

The alluvium is the principal aquifer in the lower Tonto Creek basin and yields large quantities of water to wells. The unit receives recharge from infiltration of flow in Tonto Creek and its tributaries and discharges about 4, 000 acre-feet of water annually to Roosevelt Lake. Water lost from the alluvium by evapotranspiration is estimated to be 13,000 acre-feet per year and is estimated to average 2. 6 acre - feet per acre per year in the 5, 080~acre channel and flood plain of lower Tonto Creek.

Ground-water discharge by subsurface outflow, evapotranspira­tion, and pumping from wells lowers the water level in the alluvium below the level of the streambed during part of the year, which provides space for streamflow to infiltrate and recharge the ground- water reservoir. Stream­flow continues to infiltrate until the aquifer is filled to the level ofthe stream­bed. Most of the recharge to the ground-water reservoir occurs from the infiltration of winter runoff.

The estimated annual volume of infiltration of 20, 000 acre - feet from Tonto Creek and its tributaries is slightly larger than the combined estimated annual volumes of subsurface outflow and evapotranspiration of 17, 000 acre-feet. The estimated infiltration rates were applied to the flow­duration curve for Tonto Creek above Gun Creek and were computed mainly from data collected when the flow in Tonto Creek was fairly constant and when there was no known tributary inflow. Under these conditions, a sufficient volume of unsaturated aquifer material probably is available to accept the infiltration. When the flow in Tonto Creek is large for a prolonged period, however, the volume of unsaturated aquifer material probably decreases to a point where infiltration rates are reduced significantly. Under these con­ditions, the infiltration rates probably are overestimated, and the amount of surface flow to Roosevelt Lake probably is larger. Therefore, the actual average annual volume of infiltration along lower Tonto Creek probably is about 17, 000 acre-feet.

The similarity between the chemic al composition of the streamflow in lower Tonto Creek and that of the ground water in the alluvium indicates that this aquifer receives most of its recharge from infiltration of stream­flow. The water from Tonto Creek and the ground water in the alluvium are of excellent chemical quality and are suitable for most uses. The lower part of the basin fill yields small quantities of water to wells in the northern part of the area and is potentially a significant aquifer. Water from this unit is of excellent chemical qua lit Y and is similar in chemical composition to water in the alluvium. Water from a well drilled in the fine- grained facies of the upper part of the basin fill near Punkin Center contains large concen­trations of sodium and sulfate, and the arsenic content of 0.21 mg/l and the fluoride content of 3, a mg/l exceed the man d at 0 r y rejection limits for drinking water.

38

REFERENCES CITED

Blaney, H. F., and Criddle, W. D., 1962, Determining consumptive use and irrigation water requirements: U.S. Dept. Agriculture Tech. Bull. 1275, 59 p.

Burkham, D. E., 1970, Depletion of streamflow by infiltration in the main channels of the Tucson basin, southeastern Arizona: U. S. Geol. Survey Water-Supply Paper 1939-B, 36 p.

Cruff, R. W., and Thompson, T. H., 1967, A comparison of methods of estimating potential evapotranspiration from climatological data in arid and subhumid environments: U. S. Geol. Survey Water­Supply Paper 1839-M, 28 p.

Feth, J. H., and Hem, J. D., 1963, Reconnaissance of headwater springs in the Gila River drainage basin, Arizona: U. S. Geol. Survey Water-Supply Paper 1619-H, 54 p.

Green, C. R., and Sellers, W. D., eds., 1964, Arizona climate: Tucson, Univ. Arizona Press, 503 p.

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